Studies to date indicate that Percutaneous Endoscopic Gastrostomy (PEG) and Non-Invasive Positive Pressure Ventilation (NIPPV) improve survival in Amyotrophic Lateral Sclerosis (ALS), even though introduced late in the disease. We hypothesize that early intervention may improve outcome even further. However, many issues regarding the early use of these treatments preclude the design of a Phase III clinical trial to test this hypothesis. Common to both NIPPV and nutrition is a lack of a reliable indicator of early respiratory or nutritional insufficiency. With respect to nutrition, we need reliable and cost effective methods to determine a patient's energy (i.e. caloric) requirements during different stages of the illness and base the recommendation for PEG on the adequacy of energy intake. For NIPPV, we need to identify factors that influence acceptance and tolerability of this therapy, and measurements of early respiratory dysfunction. Therefore, we propose this multicenter Pilot Study to develop methods for a definitive Phase III trial. The Specific Aims of this Pilot Study are: 1) To develop and validate strategies to improve tolerability of NIPPV, to identify factors that influence acceptance of this treatment modality, and to evaluate measures of early respiratory dysfunction; and 2) To develop and validate methods to determine energy balance in ALS. In this Pilot Study, all 11 sites will enroll patients using a stratified design based on FVC (80-95% vs 50-79%) and offer NIPPV as they decline to the lower limit of this FVC level. Six sites will collect additional detailed information to critically evaluate acceptability of NIPPV, devise strategies to improve tolerance, and validate this approach as well as collect respiratory measurements that may allow earlier identification of failure. The other 5 sites will use the "gold standard" Doubly Labeled Water method in a longitudinal design to derive empiric equations to reliably predict individual energy needs based on easily performed clinical measures. The results of this Pilot Study will allow us to develop and validate methods so that we can design a multicenter Phase III trial to determine the efficacy of early NIPPV and nutritional intervention. In addition, our results will be immediately applicable for use by clinicians in practice and will provide the basis to re-formulate the experimental design of future drug trials in ALS.